Also because newer generations just aren’t sold on diamonds being a luxury item anymore. Your average Joe just isn’t paying their rent or more on a diamond engagement/wedding ring like they used to because, well, that’s their rent payment or mortgage for something that’s gonna lose value the second they walk out of the store.
Industrial diamonds have always been on the cheap and that industry is far removed from the jewelry/gem industry, in fact a large majority of diamonds that are mined aren’t gem grade, they’re industrial grade. It’s been growing and advancing despite the jewelry/gem market starting to fall.